Messages in this thread Patch in this message | | | Subject | Re: [PATCH net] tuntap: raise EPOLLOUT on device up | From | Jason Wang <> | Date | Tue, 22 May 2018 11:22:11 +0800 |
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On 2018年05月22日 06:08, Michael S. Tsirkin wrote: > On Mon, May 21, 2018 at 11:47:42AM -0400, David Miller wrote: >> From: Jason Wang <jasowang@redhat.com> >> Date: Fri, 18 May 2018 21:00:43 +0800 >> >>> We return -EIO on device down but can not raise EPOLLOUT after it was >>> up. This may confuse user like vhost which expects tuntap to raise >>> EPOLLOUT to re-enable its TX routine after tuntap is down. This could >>> be easily reproduced by transmitting packets from VM while down and up >>> the tap device. Fixing this by set SOCKWQ_ASYNC_NOSPACE on -EIO. >>> >>> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org> >>> Cc: Eric Dumazet <edumazet@google.com> >>> Fixes: 1bd4978a88ac2 ("tun: honor IFF_UP in tun_get_user()") >>> Signed-off-by: Jason Wang <jasowang@redhat.com> >> I'm no so sure what to do with this patch. >> >> Like Michael says, this flag bit is only checks upon transmit which >> may or may not happen after this point. It doesn't seem to be >> guaranteed.
The flag is checked in tun_chr_poll() as well.
> Jason, can't we detect a link up transition and respond accordingly? > What do you think? >
I think we've already tried to do this, in tun_net_open() we call write_space(). But the problem is the bit may not be set at that time.
A second thought is to set the bit in tun_chr_poll() instead of -EIO like:
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index d45ac37..46a1573 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1423,6 +1423,13 @@ static void tun_net_init(struct net_device *dev) dev->max_mtu = MAX_MTU - dev->hard_header_len; }
+static bool tun_sock_writeable(struct tun_struct *tun, struct tun_file *tfile) +{ + struct sock *sk = tfile->socket.sk; + + return (tun->dev->flags & IFF_UP) && sock_writeable(sk); +} + /* Character device part */
/* Poll */ @@ -1445,10 +1452,9 @@ static __poll_t tun_chr_poll(struct file *file, poll_table *wait) if (!ptr_ring_empty(&tfile->tx_ring)) mask |= EPOLLIN | EPOLLRDNORM;
- if (tun->dev->flags & IFF_UP && - (sock_writeable(sk) || - (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) && - sock_writeable(sk)))) + if (tun_sock_writeable(tun, tfile) || + (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) && + tun_sock_writeable(tun, tfile))); mask |= EPOLLOUT | EPOLLWRNORM;
if (tun->dev->reg_state != NETREG_REGISTERED) Does this make more sense?
Thanks
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